Amyloidosis refers to a collection of conditions, disorders, and diseases associated with abnormal deposition of amyloidal protein. For instance, Alzheimer's disease is believed to be caused by abnormal deposition of amyloidal protein in the brain. Thus, these amyloidal protein deposits, otherwise known as amyloid-beta peptide, A-beta, or betaA4, are the result of proteolytic cleavage of the amyloid precursor protein (APP).
The majority of APP molecules that undergo proteolytic cleavage are cleaved by the aspartyl protease alpha-secretase. Alpha-secretase cleaves APP between Lys687 and Leu688 producing a large, soluble fragment, alpha-sAPP, which is a secreted form of APP that does not result in beta-amyloid plaque formation. The alpha-secretase cleavage pathway precludes the formation of A-beta, thus providing an alternate target for preventing or treating amyloidosis.
Some APP molecules, however, are cleaved by a different aspartyl protease known as beta-secretase which is also referred to in the literature as BACE, BACE1, Asp2, and Memapsin2. Beta-secretase cleaves APP after Met671, creating a C-terminal fragment. See, for example, Sinha et al., Nature, (1999), 402:537-554 and published PCT application WO 00/17369. After cleavage of APP by beta-secretase, an additional aspartyl protease, gamma-secretase, may then cleave the C-terminus of this fragment, at either Val711 or Ile713, (found within the APP transmembrane domain), generating an A-beta peptide. The A-beta peptide may then proceed to form beta-amyloid plaques. A detailed description of the proteolytic processing of APP fragments is found, for example, in U.S. Pat. Nos. 5,441,870, 5,721,130, and 5,942,400.
The amyloidal disease Alzheimer's is a progressive degenerative disease that is characterized by two major pathologic observations in the brain which are (1) neurofibrillary tangles, and (2) beta-amyloid (or neuritic) plaques. A major factor in the development of Alzheimer's disease is A-beta deposits in regions of the brain responsible for cognitive activities. These regions include, for example, the hippocampus and cerebral cortex. A-beta is a neurotoxin that may be causally related to neuronal death observed in Alzheimer's disease patients. See, for example, Selkoe, Neuron, 6 (1991) 487. Since A-beta peptide accumulates as a result of APP processing by beta-secretase, inhibiting beta-secretase's activity is desirable for the treatment of Alzheimer's disease.
Dementia-characterized disorders also arise from A-beta accumulation in the brain including accumulation in cerebral blood vessels (known as vasculary amyloid angiopathy) such as in the walls of meningeal and parenchymal arterioles, small arteries, capillaries, and venules. A-beta may also be found in cerebrospinal fluid of both individuals with and without Alzheimer's disease. Additionally, neurofibrillary tangles similar to the ones observed in Alzheimer's patients can also be found in individuals without Alzheimer's disease. In this regard, a patient exhibiting symptoms of Alzheimer's due to A-beta deposits and neurofibrillary tangles in their cerebrospinal fluid may in fact be suffering from some other form of dementia. See, for example, Seubert et al., Nature, 359 (1992) 325-327. Examples of other forms of dementia where A-beta accumulation generates amyloidogenic plaques or results in vascular amyloid angiopathy include Trisomy 21 (Down's Syndrome), Hereditary Cerebral Hemorrhage with amyloidosis of the Dutch-Type (HCHWA-D), and other neurodegenerative disorders. Consequently, inhibiting beta-secretase is not only desirable for the treatment of Alzheimer's, but also for the treatment of other conditions associated with amyloidosis.
Amyloidosis is also implicated in the pathophysiology of stroke. Cerebral amyloid angiopathy is a common feature of the brains of stroke patients exhibiting symptoms of dementia, focal neurological syndromes, or other signs of brain damage. See, for example, Corio et al., Neuropath Appl. Neurobiol., 22 (1996) 216-227. This suggests that production and deposition of A-beta may contribute to the pathology of Alzheimer's disease, stroke, and other diseases and conditions associated with amyloidosis. Accordingly, the inhibition of A-beta production is desirable for the treatment of Alzheimer's disease, stroke, and other diseases and conditions associated with amyloidosis.
Presently there are no known effective treatments for preventing, delaying, halting, or reversing the progression of Alzheimer's disease and other conditions associated with amyloidosis. Consequently, there is an urgent need for methods of treatment capable of preventing and treating conditions associated with amyloidosis including Alzheimer's disease.
Likewise, there is a need for methods of treatment using compounds that inhibit beta-secretase-mediated cleavage of APP. There is also a need for methods of treatment using compounds that are effective inhibitors of A-beta production, and/or are effective at reducing A-beta deposits or plaques, as well as methods of treatment capable of combating diseases and conditions characterized by amyloidosis, or A-beta deposits, or plaques.
There is also a need for methods of treating conditions associated with amyloidosis using compounds that are efficacious, bioavailable and/or selective for beta-secretase. An increase in efficacy, selectivity, and/or oral bioavailability may result in preferred, safer, less expensive products that are easier for patients to use.
There is also a need for methods of treating at least one condition associated with amyloidosis using compounds with characteristics that would allow them to cross the blood-brain-barrier. Desirable characteristics include a low molecular weight and a high log P (increased log P=increased lipophilicity).
Generally, known aspartyl protease inhibitors are either incapable of crossing the blood-brain barrier or do so with great difficulty. These compounds are unsuitable for the treatment of the conditions described herein. Accordingly, there is a need for methods of treating at least one condition associated with amyloidosis using compounds that can readily cross the blood-brain barrier and inhibit beta-secretase.
There is also a need for a method of finding suitable compounds for inhibiting beta-secretase activity, inhibiting cleavage of APP, inhibiting production of A-beta, and/or reducing A-beta deposits or plaques.
The present invention is directed to novel compounds and also to methods of treating at least one condition, disorder, or disease associated with amyloidosis using such compounds. An embodiment of the present invention is compounds of formula (I) or at least one pharmaceutically acceptable salt thereof, wherein R1, R2, and RC are defined below. Another embodiment of the present invention is a method of administering at least one compound of formula (I) or at least one pharmaceutically acceptable salt thereof, wherein R1, R2, and RC are defined below, in treating at least one condition, disorder, or disease associated with amyloidosis. Another embodiment is directed to methods of treatment comprising administering at least one compound of formula (I) or at least one pharmaceutically acceptable salt thereof, wherein R1, R2, and RC are defined below, useful in preventing, delaying, halting, or reversing the progression of Alzheimer's disease.
Another embodiment of the present invention is directed to uses of beta-secretase inhibitors of at least one compound of formula (I) or at least one pharmaceutically acceptable salt thereof, wherein R1, R2, and RC are defined below, in treating or preventing at least one condition, disorder, or disease associated with amyloidosis.
Another embodiment of the present invention is the administration of beta-secretase inhibitors of at least one compound of formula (I) or at least one pharmaceutically acceptable salt thereof, wherein R1, R2, and RC are defined below, exhibiting at least one property chosen from improved efficacy, bioavailability, selectivity, and blood-brain barrier penetrating properties. The present invention accomplishes one or more of these objectives and provides further related advantages.